Detective stories are largely a matter of dressing, of seasoning; of putting flesh on the bones of the whodunit, of coloring between the lines. They are as much or more about the who, the where and the when as they are about the how and the why: The English manor house or the American mean street, the dandified Belgian or the medieval monk. There are, after all, only so many reasons people kill one another — murder being the subject of most all mysteries — and only so many ways to do it, and Agatha Christie has already used them all.

And so every detective story is a kind of travelogue too. "Zen," which begins Sunday night as a presentation of PBS' "Masterpiece Mystery," takes us to Italy, and not some remote, movie-magical evocation of the place, but the place itself. Both as twisty mystery and armchair vacation, it's a good way to pass a summer night.

Aurelio Zen (Rufus Sewell) is a police detective of Venetian extraction working in Rome — this subtle foreignness matters, if only to underline the fact that as an honest copper he is morally out of step with many of his colleagues and Italian officialdom in general. (He will lie on occasion, but it is always a lie for the good.) His reputation for integrity is explicitly and repeatedly stressed, though never by Zen himself, and usually to some ironic effect ("Your scruples do you credit, detective, but, really it's no way to get ahead, is it?") and it leads powerful types to try to make use of him whenever their hands need to look clean. But his successes allow him to manipulate them in turn.

The series, which has already ended its run in Britain, comes from the producers of the Sweden-set "Wallander." (Executive producer Andy Harries has used the phrase "upmarket detective franchise" to describe these shows.) As in "Wallander," the visuals are a little overworked, but the fashion-mag aesthetic here fits the milieu. The setting is contemporary, but the feel is retro; the soundtrack evokes the 1960s and '70s, by way of Mancini and Rota; the female characters could walk straight into "La Dolce Vita" or "L'Avventura" without a change of hair or dress, while Sewell has something of Marcello Mastroianni's sad-eyed, sleepy allure. His dark suits are sharp enough to cut paper edgeways, but the person who fills them is a little rumpled and rueful.

Sewell is well used here. I haven't read the Michael Dibdin novels on which "Zen" is based — the three feature-length episodes are taken from the first three books in the series, though presented in a different order — but a little research suggests that he is playing a somewhat younger, temperamentally lighter character than exists on the page. He is sweet but serious, self-possessed but only human, and in his shy, which is not to say coy, approach to a romance with coworker and immediately recognizable soul mate Caterina Murino (bringing the lone Italian accent), he is, among the wolves, refreshingly courteous.